Scientists have not yet identified the fault that ruptured in New Jersey on April 5 and shook much of the Northeast.
Now, US Geological Survey researchers are in the process of installing new monitoring equipment to better measure aftershocks and help solve this mystery.
The USGS has recorded at least 50 aftershocks since last Friday’s 4.8 magnitude earthquake. The federal agency announced Thursday that it is installing five new seismographs within a few miles of the earthquake site to monitor future rumors.
“With the new data, we should definitely be able to see on which fault these earthquakes are occurring. Whether it’s a mapped fault or not is hard to say,” said Oliver Boyd, a USGS research geologist who lives in Golden, Colorado. “They will give us a picture of what the fault network looks like, and if it happens to cause a larger earthquake, we will have instruments in the area to capture that.”
A group of researchers from the University of Texas, Rutgers University, Yale University and Columbia University are also installing 20 additional seismographs to help with efforts to map the fault network, he said.
The earthquake, which shook buildings from Maryland to Maine, was the strongest in New Jersey in more than 200 years.
It left no ruptures on the surface, Boyd explained, and the use of lidar, or light detection and ranging — technology — which uses laser pulses to detect hidden geological features — didn’t reveal anything conclusive about where exactly the earthquake occurred.
The fault system where it likely originated contains a confusing collection of fissures that are remnants of ancient tectonic processes. Seismologists say slow-acting stress likely triggered the earthquake.
“We may never know under what fault this occurred,” Boyd said.
He added that the USGS typically monitors aftershocks after any earthquake of magnitude 5.0 or greater. The agency made an exception in this case.
“Being so close to a major population center increased our interest in this particular fault and these earthquakes,” Boyd said. “In the central and eastern U.S., it’s rare to achieve something of this magnitude.”
USGS funding for the Lamont-Doherty Cooperative Seismographic Network, a regional network of monitoring equipment in the Northeast, has been cut in 2019. Because the network lost that federal funding, less than half of its 45 stations were operating when the 4.8 magnitude earthquake occurred. More data from the network may have helped researchers pinpoint the earthquake’s location.
“The closest station was 75 kilometers away before we installed these stations,” Boyd said, referring to the new seismometers the USGS is deploying. (That’s a distance of about 75 kilometers.) “Knowing exactly where these earthquakes were located was difficult.”
Since the earthquake, at least one station on the Lamont regional network has been reactivated, he said.
Boyd added that the pattern of aftershocks since the event has been typical and there have been fewer than initially expected. Aftershocks that can be felt by people — with magnitudes in the “upper two” and higher — will likely continue for another week, he said. Minor aftershocks can persist for months.
Additional USGS seismometers are expected to remain in New Jersey for three to six months.
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